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From: gnb@bby.oz.au (Gregory N. Bond)
Newsgroups: comp.lang.perl,comp.sources.bugs
Subject: BUG in interpolating and/or substituting NULs in strings?
Message-ID: <GNB.91May21123118@leo.bby.oz.au>
Date: 21 May 91 02:31:18 GMT
Article-I.D.: leo.GNB.91May21123118
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Consider this fragment of code, which is extracted from a script I am
writing to parse and interpret a data feed that has the following format:

	SOH
	header
	STX
	data
	ETX
	2 bcc characters
	optional NUL

I was using $/ = SOH to split the lines as the nul was not necessarily
present, so the line ended with ETX, 2 characters, potential NUL, SOH.

I inserted some diagnostics to asci-fy the input data and got random
results.  A much-cutdown version is shown below, with results.  Note
that the string "^@" in the output is a literal NUL character (i.e.
hex 0x0) that I have converted for news.

Script started on Tue May 21 12:14:06 1991
leo% cat t.perl
#! /usr/local/bin/perl

$NUL = "\0";
$SOH = "\1";
$STX = "\2";
$ETX = "\3";

$_ = "data a${STX}data b${ETX}cc${NUL}${SOH}";

	$p = $_;
	$p =~ s/$ETX/<ETX>/og;
	$p =~ s/$STX/<STX>/og;
	$p =~ s/$SOH/<SOH>/og;
	$p =~ s/$NUL/<NUL>/og;
	print "[$p]\n";

	$p = $_;
	$p =~ s/$NUL/<NUL>/og;
	$p =~ s/$SOH/<SOH>/og;
	$p =~ s/$STX/<STX>/og;
	$p =~ s/$ETX/<ETX>/og;
	print "[$p]\n";

leo% perl -v

This is perl, version 4.0

$RCSfile: perl.c,v $$Revision: 4.0.1.1 $$Date: 91/04/11 17:49:05 $
Patch level: 3

Copyright (c) 1989, 1990, 1991, Larry Wall

Perl may be copied only under the terms of the GNU General Public License,
a copy of which can be found with the Perl 4.0 distribution kit.
leo% perl t.perl
[data a<STX>data b<ETX>cc^@<SOH>]
[data a<STX>data b<ETX>cc^@<NUL>]
leo% ^D
script done on Tue May 21 12:14:22 1991

The output should be the same independent of the order in which the
substitutions are done, and the literal NUL should have gone.

Is this a bug or am I out to lunch here?

Environment is Solbourne OS/MP 4.0D (equiv to Sun4 / SunOs 4.0.3) with
the system compiler and all defaults in config.  Also happens with
perl compiled on a Sun 3/60, SunOs 4.0.3.

Greg.
--
Gregory Bond, Burdett Buckeridge & Young Ltd, Melbourne, Australia
Internet: gnb@melba.bby.oz.au    non-MX: gnb%melba.bby.oz@uunet.uu.net
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